Disposable electrode with a metallurgically-bonded,silver-silver chloride sensing element

ABSTRACT

A DISPOSABLE ELECTRODE IS PROVIDED FOR BIOLOGICAL AND MEDICAL USE COMPRISING A SENSING ELEMENT HOUSING FORMED OF AN INSULATING MATERIAL AND HAVING SURFACES THEREON ADAPTED TO RECEIVE AND RETAIN A SENSING ELEMENT AND A SENSING ELEMENT. THE SENSING ELEMENT COMPRISES A UNI-   FORMLY THICK FLAT LAYER OF SILVER TO WHICH A UNIFORMLY THICK FLAT LAYER OF SILVER CHLORIDE IS METALLURGICALLY BONDED.

March 23, 1971 YUAN 3,572,323

' DISPOSABLE ELECTRODE WITH A METALLURGICALLY-BONDED,

SILVER-SILVER CHLORIDE SENSING ELEMENT Filed Jan. 5, 1969 fFP/W/K 4.run/v BY AAQ4-LE K MTM ATTORNEYS United States Patent DISPOSABLEELECTRODE WITH A METALLURGI- CALLY-BONDED, SILVER-SILVER CHLORIDESENSING ELEMENT Frank L. Yuan, Wayland, Mass., assignor, to Becton,Dickinson and Company, East Rutherford, NJ. Filed Jan. 3, 1969, Ser. No.788,828 Int. Cl. A61b 5/04 U.S. Cl. 1282.06 6 Claims ABSTRACT OF THEDISCLOSURE A disposable electrode is provided for biological and medicaluse comprising a sensing element housing formed of an insulatingmaterial and having surfaces thereon adapted to receive and retain asensing element and a sensing element. The sensing element comprises auniformly thick flat layer of silver to which a uniformly thick fiatlayer of silver chloride is metallurgically bonded.

BACKGROUND OF THE INVENTION Electrodes find extensive use in the medicaland related fields to transform biopotentials into electrical signalswhich may be monitored for a variety of functions, such aselectrocardiographs, electroencephalographs, or electromyograms. Suchelectrodes are usually placed on the skin of the patient whose functionis to be monitored with an interposed layer of a suitable electrolyte,generally in gel form. Ion flow passes through the subjects skin and theelectrolyte to react with the electrode and generate an electricalsignal which is then monitored.

One electrode construction which affords relative stability, lowimpedance, and low offset voltage, and is therefore particularly wellsuited for medical purposes utilizes a silver-silver chloride sensingelement. Heretofore, such silver-silver chloride electrodes weregenerally formed either by compressing a mixture of silver andsilver-chloride powders, occasionally with small quantities of a bindersuch as bentonitic clay added, or by mechanically coupling sheets ofsilver and silver-chloride to one another.

Although such electrodes have generally performed well from a technicalpoint of view, in most applications, the high cost associated with theirconstruction has prevented their extensive use, particularly whereelectrode contamination is a problem and disposability is desirable orrequired. Further, the impedance of such prior art electrodes is higherthan required or desired for most applications and the effectiveness ofthe mechanical bond between the silver and silver chloride molecules mayvary with movement of the patient, thereby varying the electrodeimpedance resulting in variations in the accuracy of the electrodereadout. Also, the electrical characteristics of these prior artelectrodes usually varied considerably from electrode to electrode andhence interchangeability was not possible unless the monitoringequipment was recalibrated for each electrode.

SUMMARY OF THE INVENTION It is, therefore, the principal object of thepresent invention to provide an improved disposable electrode havingacceptable electrical characteristics including low impedance andpolarization voltage which is lightweight, reliable, compact,sufiiciently inexpensive to reasonably permit single use, and which isinterchangeable with other similarly manufactured electrodes.

These and other beneficial objects and advantages are attained inaccordance with the present invention by providing an electrodecomprising a sensing element housing including a generally flat memberformed of an insulating ice material and having a depressed centerportion integral with a raised peripheral portion, and a sensing elementdisposed within the depression. The sensing element comprises a first,uniformly thick, flat layer of silver to which a uniformly thick, flatlayer of silver-chloride is metallurgically bonded. An intermediatelayer is interposed between the silver and silver-chloride layers and iscoextensive therewith and forms a zone wherein difiusion of the silverand silver-chloride molecules occurs while preventing any slippagebetween the silver and silverchloride layers. The sensing element isdisposed within the housing depression with the silver layer abuttingthe rear surface of the depression. An electrically conductive leadhaving one end in electrical contact with the silver layer and the otherend adapted to be coupled to the monitoring equipment is also provided.The raised peripheral portion of the housing also includes a continuousdouble sided adhesive adapted to facilitate adhering the electrode tothe subject.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 is a top plan view of the electrode of the present invention;

FIG. 2 is a side elevational sectional view taken along reference line2-2 of FIG. 1; and

FIG. 3 is a fragmentary diagrammatic view of portions of the sensingelement of the electrode of the present invention greatly magnified.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Reference is now madeto the drawings wherein like parts are designed by similar referencenumerals throughout the several views. In FIG. 1, the electrode 10 ofthe present invention is depicted as comprising a housing 12, a sensingelement 14 disposed within the housing, an electrical lead 16 extendingbetween the sensing element 14 and a terminal portion 18, anda.terrninal portion 18 which includes a connector 20 which in thispreferred embodiment, is a snap-fit female connector adapted to besnapped into place about a suitable male connector.

The housing 12 is formed of an insulating material such as polyethyleneor polypropylene which is readily moldable into the desired shape. .Inthis case, the housing comprises a generally flat member having adepressed center portion 22- and a peripheral portion 24 raised withrespect to the center portion 22 and spaced from the center portion bythe conical frustum Wall member 26 'which extends between the twoportions of the housing.

The inner surfaces 28 and 30 of wall member 26 and depressed centerportion 22, respectively, thus define an open ended chamber 32- theopening 34 of which is further defined by the inner edge 36 of theraised peripheral portion 24. In this regard, and as best seen in FIG.2, the raised peripheral portion 24 comprises, in essence, an annulardisc and the raised edge 36 is defined by the inner radius of the disc.

A double sided adhesive strip 38 is disposed about the outer face of theraised peripheral portion 24. One side of adhesive 38 adheres to theouter face of the housing and the other side is adapted to be adhered tothe body of the subject under observation, thereby forming means forcoupling the electrode to the subject. In this regard, a backing strip40 is disposed about the free face of the double sided adhesive toprotect the tackiness of the adhesive prior to use. A tab 42 extendsfrom the outer peripheral edge of the backing strip to facilitate itsremoval and the application of the electrode to the subject.

The inner surface 30 of the depressed center portion of the housing 12is further defined by a circular recessed section 44 into which thesensing element 14 is fitted.

A hole 46 extends through the center of recess 44 to the outer surfaceof the housing and the conductive wire 48 of electrical lead 16 extendsthrough hole 46 to make electrical contact with the rear of the sensingelement 14. After the sensing element is positioned within recess 44 andthe electrical contact is established between the sensing element 14 andlead 16 as by soldering, a suitable potting compound, as for exampleepoxy, is applied to the rear of the housing filling hole 46 and therebyserving to form bead 50 which protects the electrical contact betweenthe lead and sensing element and also serves to secure the sensingelement 14 within the housing 12.

The sensing element .14 comprises agenerally circular disc, the diameterof which is substantially the same as that of recess 44 having raisedside walls 52 which are substantially equal to the depth of the recess.The sensing element comprises a first flat layer 54 of silver to which alayer of silver chloride 56 has been metallurgically bonded as forexample, by the process disclosed in US. Letters Patent No. 3,059,331for Method of Making Composite Stock which issued on Oct. 23, 1962 andis assigned to the Texas Instruments Corporation. The metallurgical bondbetween the silver and silver-chloride layers 54 and 56, respectively,results in the formation of an interposed diffused third layer 58comprising both silver and silver-chloride molecules. Thecross-sectional configuration of the sensing element =14 is depicted inFIG. 3 in exaggerated diagrammatic form. In a successful practice of thepresent invention, the thickness of the sensing element was two milswith the silver chloride portion comprising of the total composite orapproximately .3 mil. The individual sensing elements 14 are formed byproperly stamping or cutting a sheet of composite stock. Since thethicknesses of the silver and silver chloride layers of the compositematerial may be accurately maintained throughout the stock and alsosince a firm metallurgical bond is maintained between the compositelayers, the electrical characteristics of two such electrodes will besubstantially identical, thus penmitting the interchangeability of theelectrodes.

The sensing element 14 is positioned within housing 12 with the silverlayer 14 abutting the housing and making electrical contact with theconducting lead 48 and the silver chloride layer 56* directed toward thehousing opening 34. That is, when viewing the front of electrode 10, allthat will be seen is the silver chloride surfaces 56 of the sensingelement 14.

In use, the open ended chamber 32 is filled to the brim with anelectrolyte such as a salt gel whereafter the backing strip 42 isremoved from the face of adhesive 38 and the electrode is appropriatelypositioned on the subject. The terminal portion 18 of the electrode isthen connected to suitable monitoring equipment with the connector 20coupled to a mating connector associated with the monitoring equipment.Electrical signals transmitted from the subject will be transmittedthrough the electrolyte to the sensing element and then to themonitoring equipment. After use, the electrode may be disposed of and inthis regard, it will be economically feasible to discard an electrodeproduced in accordance with the present invention after a single use.

Having thus described my invention, what I claim is:

1. A disposable electrode comprising: a sensing element housing formedof an insulating material and having first surfaces adapted to bemounted to the subject being monitored and second surfaces spaced apartfrom said first surfaces to receive and retain the sensing element; asensing element mounted to said housing second surfaces and comprising auniformly thick fiat layer of silver and a uniformly thick flat layer ofsilver-chloride coextensive with said first layer and metallurgicallybonded thereto; and, an electrically conductive lead in electricalcontact with said silver layer of said sensing element and adapted to becoupled to associated monitoring equipment.

2. The invention in accordance with claim -1 wherein said sensingelement further includes an intermediary layer interposed between saidsilver layer and said silver chloride layer and coextensive therewithwherein diffusion of silver and silver chloride molecules occurs in saidintermediate layer whereby to effect said metallurgical bond.

3. The invention in accordance with claim 1 wherein said housingcomprises a molded plastic material.

4. The invention in accordance with claim 3 wherein said housingcomprises a generally flat member having a depressed center portiondefining said housing second surfaces integral with a raised peripheralportion defining said housing first-surfaces and said sensing element ismounted at the base of said depressed portion with said silver chloridelayer directed toward said raised peripheral portion.

5. The invention in accordance with claim 1 further comprising a doublefaced adhesive disposed about said first surfaces.

6. The invention in accordance with claim 1 wherein said silver layer issubstantially two mils in thickness and said silver-chloride layer issubstantially .3 mil in thickness.

References Cited UNITED STATES PATENTS 3,420,223 1/1969 Day et a11282.06

WILLIAM E. KAMM, Primary Examiner

